/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the  "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id$
 */
package wx.xml.xalan.xpath.operations;

import wx.xml.xalan.xpath.Expression;
import wx.xml.xalan.xpath.ExpressionOwner;
import wx.xml.xalan.xpath.XPathContext;
import wx.xml.xalan.xpath.XPathVisitor;
import wx.xml.xalan.xpath.objects.XObject;

/**
 * The baseclass for a binary operation.
 */
public class Operation extends Expression implements ExpressionOwner {
    static final long serialVersionUID = -3037139537171050430L;

    /**
     * The left operand expression.
     *
     * @serial
     */
    protected Expression m_left;

    /**
     * The right operand expression.
     *
     * @serial
     */
    protected Expression m_right;

    /**
     * This function is used to fixup variables from QNames to stack frame
     * indexes at stylesheet build time.
     *
     * @param vars List of QNames that correspond to variables.  This list
     *             should be searched backwards for the first qualified name that
     *             corresponds to the variable reference qname.  The position of the
     *             QName in the vector from the start of the vector will be its position
     *             in the stack frame (but variables above the globalsTop value will need
     *             to be offset to the current stack frame).
     */
    public void fixupVariables(java.util.Vector vars, int globalsSize) {
        m_left.fixupVariables(vars, globalsSize);
        m_right.fixupVariables(vars, globalsSize);
    }


    /**
     * Tell if this expression or it's subexpressions can traverse outside
     * the current subtree.
     *
     * @return true if traversal outside the context node's subtree can occur.
     */
    public boolean canTraverseOutsideSubtree() {

        if (null != m_left && m_left.canTraverseOutsideSubtree())
            return true;

        if (null != m_right && m_right.canTraverseOutsideSubtree())
            return true;

        return false;
    }

    /**
     * Set the left and right operand expressions for this operation.
     *
     * @param l The left expression operand.
     * @param r The right expression operand.
     */
    public void setLeftRight(Expression l, Expression r) {
        m_left = l;
        m_right = r;
        l.exprSetParent(this);
        r.exprSetParent(this);
    }

    /**
     * Execute a binary operation by calling execute on each of the operands,
     * and then calling the operate method on the derived class.
     *
     * @param xctxt The runtime execution context.
     * @return The XObject result of the operation.
     * @throws javax.xml.transform.TransformerException
     */
    public XObject execute(XPathContext xctxt)
        throws javax.xml.transform.TransformerException {

        XObject left  = m_left.execute(xctxt, true);
        XObject right = m_right.execute(xctxt, true);

        XObject result = operate(left, right);
        left.detach();
        right.detach();
        return result;
    }

    /**
     * Apply the operation to two operands, and return the result.
     *
     * @param left  non-null reference to the evaluated left operand.
     * @param right non-null reference to the evaluated right operand.
     * @return non-null reference to the XObject that represents the result of the operation.
     * @throws javax.xml.transform.TransformerException
     */
    public XObject operate(XObject left, XObject right)
        throws javax.xml.transform.TransformerException {
        return null;  // no-op
    }

    /**
     * @return the left operand of binary operation, as an Expression.
     */
    public Expression getLeftOperand() {
        return m_left;
    }

    /**
     * @return the right operand of binary operation, as an Expression.
     */
    public Expression getRightOperand() {
        return m_right;
    }

    /**
     * @see wx.xml.xalan.xpath.XPathVisitable#callVisitors(ExpressionOwner, XPathVisitor)
     */
    public void callVisitors(ExpressionOwner owner, XPathVisitor visitor) {
        if (visitor.visitBinaryOperation(owner, this)) {
            m_left.callVisitors(new LeftExprOwner(), visitor);
            m_right.callVisitors(this, visitor);
        }
    }

    /**
     * @see ExpressionOwner#getExpression()
     */
    public Expression getExpression() {
        return m_right;
    }

    /**
     * @see ExpressionOwner#setExpression(Expression)
     */
    public void setExpression(Expression exp) {
        exp.exprSetParent(this);
        m_right = exp;
    }

    /**
     * @see Expression#deepEquals(Expression)
     */
    public boolean deepEquals(Expression expr) {
        if (!isSameClass(expr))
            return false;

        if (!m_left.deepEquals(((Operation) expr).m_left))
            return false;

        if (!m_right.deepEquals(((Operation) expr).m_right))
            return false;

        return true;
    }

    class LeftExprOwner implements ExpressionOwner {
        /**
         * @see ExpressionOwner#getExpression()
         */
        public Expression getExpression() {
            return m_left;
        }

        /**
         * @see ExpressionOwner#setExpression(Expression)
         */
        public void setExpression(Expression exp) {
            exp.exprSetParent(Operation.this);
            m_left = exp;
        }
    }
}
